Answer:
Independent Variable : The Person advertising
Step-by-step explanation:
REGRESSION is statistical tool to analyse relationship between Independent Variable & Dependent Variable .
Independent Variable is the Variable causing change in the Dependent Variable & the Dependent Variable is the variable being affected by Independent Variable . Eg - In Law of demand price - demand inverse relationship (more price , less demand / less price , more demand) ; Price is the independent variable affecting dependent variable Demand .
In this case : Researcher is trying to analyse impact of advertising person on sales , so advertising person is independent variable & sales are dependent variable . However , regression analysis can be with quantitative (numerical) variables - so this qualitative variable can be converted into dummy variable (1 if person is a doctor , 0 if person is a teacher)